A Current Optimization Method for Torque Ripple Reduction of Permanent Magnet Synchronous Motor with Distorted Back EMF

Demagnetization in permanent magnet synchronous motor (PMSM), caused by high temperature or reverse magnetic field, could not only reduce the back-EMF amplitude but also lead to back-EMF waveform distortion. The decrease of the amplitude will bring greater loss current, and the waveform distortion will cause torque ripple. In order to reduce the torque ripple and improve the stability of the servo control system, this paper develops a current control method to obtain the optimal current by using non-sinusoidal back EMF. Firstly, a flux observer is established, and the obtained amplitudes of flux are used to reconstruct the back EMF waveform. Then, the pseudo-inverse operation of the torque equation is performed to convert the desired torque into the optimal current as a given value of the three-phase current. The simulation results show that the method can effectively suppress the torque ripple.